ANOMALOUS
by Serifim
Summary: There's an anomaly in the Underground: an unwitting pawn to worldwide Genocide. She was only looking for her lost sibling, but what she found after the fall actually doomed her from the start. Perhaps if she'd known that all the people she began to love and care for weren't actually human, like her mind led her to be believe... perhaps then things would have been simpler.


**[* Check ]** _Yeahhh, first Undertale fanfiction_ _~ Hooopefully it's not too bad?_ _There will be a lot of spoilers by the way, especially for the Genocide Route, so please proceed with this in mind!_

 _And I deeply apologize if the first few chapters are a little slow_ _… 'cause the real adventure starts once all the formalities are out of the way. :3  
_

 _Anyway, hope you'll check this story out, and give it a fave/follow if you like it. Reviews are ALWAYS welcome, too. Thank you very much!_

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 _ **I - The Dark Below  
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 _Pain_. The pain was an insistent throb radiating outward in waves at the back of her head, along her spine, right down to the delicate tailbone… It hurt everywhere. Or, at least where her body had impacted the ground, so mostly the dorsal side. But it hurt a lot regardless.

The dark-haired young woman sniffed at a near-imperceptible scent perfuming the immediate vicinity, so light and powdery in its quality that she only fully acknowledged it after she rolled over awkwardly and received a faceful of vividly blooming flowers. Their full yellow petals were surprisingly soft and delicate to the touch, perfectly good for observation and admiration, but also poor as an adequate landing pad. They probably offered little more cushioning than would a pile of folded origami roses.

Groaning out of aggravation—and soreness—the girl toiled to extract her arms from beneath her body and thereby use them to lift herself off the floor. About halfway through the unsteady push-up her elbows balked and sent her face straight back into the flowers.

"Oww… Why me…?" She grit her teeth, one hand stroking the back of her neck, almost as if to survey for any possible breakage. "That got really bad… really fast…"

Right. She remembered, retracing her steps, it had been a fall.

 _A fall on Mt. Ebott._

"And I was… looking for someone…"

Maybe the crash landing rattled her brains a bit too, since she struggled recalling even the most recent of events. She remember her name, and who she was, but one pivotal piece of the puzzle felt glaringly absent. The young woman lay still for a moment, lost in thought, before she sat up slowly, and sensed the gears of her memory clicking into place.

"That's right… my sibling."

They had been fighting in the hours leading up to the disappearance, and she recalled her regret over a vast majority of those hurtful words and accusations. The subject matter must have been so trivial, however, that it escaped her yet. What she _did_ remember was her younger sibling running off to Mt. Ebott, where the two of them often went exploring together, and then being gone for a prolonged duration of time. Search crews headed out, the worried big sister went with, and then she slipped up somewhere along the way…

That was what the story seemed to be, up to this point. The young woman looked around every which way, searching for any other signs of life, but her vision blurred in and out from disorientation and then dizziness took over from there. She began to scour her pockets for her missing smartphone, and then rifled around blindly in the flowers, struggling with the poor illumination.

Finally the young woman paused, a heavy sigh on her lips, half-exasperated and half-chagrined, a hand raised to the longer front bangs covering her right eye.

"This doesn't help at all, does it..."

After dropping her head down a moment to rest, she looked back up and let out a different kind of sigh upon seeing a small figure standing a few feet away, at the threshold of a stone hallway. It edged closer, revealing itself as a brown-haired child in a striped blue and purple turtleneck—her sibling. If that wasn't her sibling, she didn't know who else was. It was a good thing she was able to find them down here.

They walked over at a gradual pace, and while the elder sister awaited them, she started noticing the details of the area in greater relief, from the imposingly high cavern walls to the gaping crevice high above, which allowed but a few wan streaks of shriveled light to fall into darkness.

Despite her apprehension, she paid mind to only one thing: her sibling's wellbeing. She grinned and welcomed the child with open arms, the relief washing over her something like a cooling rain released from a strained and overstuffed storm cloud.

"There you are! I was so worried, I—"

Her voice faltered when she noticed how the adolescent, though apparently unharmed, betrayed neither a single hint of emotion nor any small glimmer of recognition.

"H-hey, something wrong? You're… not still upset about before, are you? I'm sorry. I didn't mean what I said, you know…"

She brightened upon seeing the little head shake from side-to-side.

"I'm glad. So… come over here! What're you waiting for? I swear, I've never been happier to see you—you… um, you…?"

For some wildly bizarre reason far beyond any understanding, she couldn't remember her sibling's name, no matter how hard she tried. Everything else about them remained intact, but the name eluded her entirely. Was that perhaps the problem? Had they forgotten each other's names?

"It's me, Mercy; your big sister," she said quickly, following that logic. "I don't know what happened… I just can't remember your name. M-maybe we hit our heads on the way down."

"… Frisk," the child said, their voice low even against the complete quiet.

"F…Frisk…? What's that?"

"I'm Frisk," they repeated at the same volume.

Mercy giggled, at once happy and embarrassed. "Oh, of course! How I forget? I'm so sorry, Frisk. I must've hit my head too hard on the way down. Hopefully it's nothing serious."

The older sister stood and brushed both hands over her white dress shirt, which was now yellowed with pollen, and cleaned her black vest and matching jeans at the same time, since she hated how the bright grains contrasted against the cloth. Then again, her dark hair was probably a polleny mess as well.

"Anyway, at least you're here and safe and sound. Let's try to find our way back. Auntie's probably still out there looking for us. …Probably."

Frisk said nothing more, instead heading out of the cavern and into an adjacent corridor, pausing only momentarily so Mercy could catch up.

"Wait, slow down a bit," she cautioned gently, peering at the gloom ahead. "This might be the way out, but we should be careful."

The two siblings passed through a wide entryway bracketed by fluted stone pillars, surmounted by a frieze carved with an unfamiliar symbol. In the next room sat a lonesome yellow flower atop a single patch of greenery, the rest of the area obscured by inky darkness. On further inspection, Mercy noticed a pair of tiny black eyes and a smiling mouth in the middle of the flower's pure white center. She was ready to make a comment when a voice cut her off.

"Howdy!" The flower actually spoke, causing Mercy to flinch. "I'm Flowey. Flowey the Flower! Hmm… You're new to the Underground, aren'tcha?"

"We… um, yes, I suppose we are."

She showed a polite smile despite her nervousness about being scrutinized by a sentient flower of all things. She glanced down at Frisk, who seemed unfazed by the sight, before looking back to Flowey.

"Golly, you must be so confused!" it said emphatically. "Someone oughta teach you how things work around here. I guess little old me will have to do! Ready? Here we go!"

"H-hold on, what…?"

Mercy tried to object, only to be stopped by a sudden, strong tug in the middle of her chest. Upon looking down she saw some sort of heart-shaped object levitating before her, its color a luminous pink, opaque at the center but growing more transparent near the edges.

"See that?" That is your SOUL," Flowey explained cheerily, "the very culmination of your being! Your SOUL starts off weak, but can grow if you gain a lot of LV."

"L…V? Does that stand for something?" Mercy questioned, confused.

"Why, LOVE, of course!" replied Flowey, with all the vim and vigor of an annoying host on a kid's TV show. "You want some LOVE, don't you? Don't worry, I'll share some with you!"

And the flower _winked_ , a little pink tongue poking out from the corner of its mouth. Mercy's ability to willingly suspend her own disbelief was faltering by the second.

"Down here," the flower continued, a number of spinning oblong shapes gathering behind it, "LOVE is shared through… little white… 'friendliness pellets.' Try moving your SOUL. Get as many as you can!"

"Oh… Hey, Frisk, isn't that ni—"

Mercy didn't even have time to finish. The so-called friendliness pellets collided with her SOUL one-by-one in quick succession. She saw the pink heart, her SOUL, flicker in and out of existence as an electric shock ran her straight through the chest, so strong and so sudden that she doubled over, gasping in surprise.

"Wh-what was that, Flowey?" she cried, her eyes watering against her will. "It hurts…!"

Flowey's smiling expression shifted from innocent to demonic in two seconds flat, the formerly cute and friendly smile now a menacing, sharp-toothed leer.

"You IDIOT. In this world, it's kill or BE killed. Why would ANYONE pass up an opportunity like this?!"

"Oh, _no_. Frisk, you've gotta ge—!"

The rest of her words were lost over the sound of bullets manifesting in a circle around both Mercy and her SOUL. Flowey stared at the young woman intently, its eyes like deep and endless wells, or hollows of madness.

"…DIE."

All Mercy could do was watch helplessly while the projectiles tightened the loop around their target, the flower now cackling with a dreadful and demonic laughter that grated like a knife on steel in her ears. There was physically no way out, no means of escape, but when she saw that Frisk had retreated safely, she was able to feel more relief than she did fear.

 _If only she could have stayed and protected her sibling longer. If only she could have protected her sibling better. If only._

Her eyes slid shut in resignation as Mercy sank to the floor, her heart clutched tightly in her hands. She never wanted this to happen. She wished she could fix it. And yet all those chances, all those opportunities, all those hopes and dreams and possibilities were being lost, irretrievably so. Her worst misgivings surfaced at the very last moment, because she knew that with death, she would never be able to give her sibling the happiness they deserved.

 _She would never get to make up for what she did to their family._

"Frisk… I'm sorry…!"

A squeaky yelp interrupted those words, and when Mercy raised her head, she saw someone else standing in Flowey's former position, and Frisk slowly coming back to her side.

The woman before them appeared to be somewhat older, around the age of Mercy's relatively young aunt, clad in flowing purple robes, her plaited hair colorless like a fresh blanket of snow, her skin almost equally pale, just barely containing the shades of pink customary in human flesh. Her face was one worn and weathered, but not hardened, by the passage of years, reflecting a firm and maternal disposition, yet also a very gentle soul, probably lively and young at heart.

Mercy saw it in her expression, too: a brimming capacity for love and true understanding. She felt a sort of gravitational pull towards this woman, a desire to know her, to stay near her, and be bathed in her warmth. Despite the unearthly hue of the woman's pink irises, she discerned genuine concern in those eyes. Perhaps that was why she felt drawn to that woman. Because she reminded Mercy of her mother.

"What a terrible creature," the woman remarked sadly to herself, "torturing these poor, innocent youths."

"Wh-who are you?" Mercy asked, her voice a bit broken, while she grabbed Frisk's hand defensively, her SOUL hovering close to her chest.

"Ah, do not be afraid, children. I am Toriel, caretaker of the ruins. I pass through this place every day to see if anyone has fallen down. You're the first humans to come here in a long time."

Mercy nodded, managing a smile despite her confusion. It was funny how she phrased that, "human", as if Toriel were not one herself. She must have been an albino, judging from the white hair and pinkish eye color, but she didn't look any less of a human woman to Mercy. Part of her felt sorry for Toriel, if she'd been living alone so long that the sight of other people came as a surprise.

"Come," said Toriel, "I will guide you through the catacombs. This way."

She turned around and proceeded to the next room, trailed by a fearless Frisk. If Frisk trusted her, Mercy would not object to it. Moreover, she noticed that her SOUL had returned to its rightful place, and she figured that it only manifested in times of need or distress. For the moment, it was safe.

For the moment, at least.

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 _(P.S. Thank you for getting down this far. :'D I appreciate your viewership! Please do me know what you think, if you have the time~ See ya.)_


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